JPS5927880B2 - How to dispose of radioactive waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the treatment of low-level radioactive waste from nuclear power plants, and more particularly to a method for effectively separating and disposing of waste ion exchange resin and radioactive cladding. .

A variety of radioactive wastes are emitted from nuclear power plants, but most of them are low-level radioactive wastes.

These wastes include liquid waste such as drain from various equipment, recycled waste liquid from desalination equipment, and washing fluid for work clothes, and used solid waste such as builter fillers and ion exchange resins.

The radionuclides that contribute to the radioactivity of these wastes are
It is mainly cobalt-60.

This depends on the corrosion products of the wetted parts of the primary cooling water system, including the reactor core.

In addition to cobalt, corrosion products include many nuclides such as iron, manganese, chromium, tungsten, sodium, zinc, and nickel, but these nuclides, with the exception of cobalt-60, have short half-lives.

Cobalt-60 has a half-life of more than five years, which poses a problem in waste treatment.

The main body of the corrosion products is iron, which exists as fine particles of oxides or hydroxides (hereinafter referred to as cladding), and cobalt is adsorbed or attached to the cladding in a concentrated form.

Cobalt-containing cladding is mixed into various liquid wastes or attached to used waste ion exchange resins, making these wastes radioactive.

In the conventional method for treating low-level liquid and solid waste, first of all, regarding liquids, the crud is separated from the equipment drain and stored in a storage tank, and the water from which the crud is separated is reused.

Floor drain, recycled waste liquid, etc. are concentrated, solidified with cement, and canned in drums.

Waste ion exchange resin is either stored in a storage tank or solidified with cement and canned in drums.

As described above, liquid and solid wastes are finally filled into drums and solidified with cement, and then stored in the storage warehouses of nuclear power plants or in storage tanks.

For example, the amount of drums filled with low-level radioactive waste generated by a nuclear power plant with a power generation capacity of 1 million KW is just under 2,000 drums per year for PWR (pressurized water type F), and less than 2,000 drums for BW.
R (boiling water reactor) is said to have 5,000 to 6,000 reactors, and with the expansion of nuclear power plants, it is predicted that the number will reach 100,000 per year and 620,000 cumulative reactors in a few years. .

Currently, these drum fills are not allowed to be dumped into the ocean and are all stored in hangars.

However, in conjunction with the progress in the development and use of nuclear energy, consideration is being given to the environmental safety assessment of ocean dumping.

Therefore, assuming that ocean dumping is permitted, it is necessary to establish a processing method that can handle ocean dumping in addition to the current storage in drum cans.

Technical standards for dumping drum-canned waste into the ocean include regulations on the mechanical strength of the drums and radiation levels.
The latter is highly dependent on the waste disposal method.

Conventionally, concentrated waste liquid has been solidified with cement and canned in drums as low-level waste, and waste ion exchange resin has been stored in storage tanks in the form of sludge.
Due to issues such as regulatory values in the case of ocean dumping, reducing the volume of these wastes and reducing radiation levels has become a major focus, and countermeasures are being considered.

For this reason, studies are being considered to solidify the concentrated waste liquid and instead of filling it with cement, which is currently the case, canning it in drums with asphalt, plastic, glass, etc.

On the other hand, waste ion-exchange resin has a considerable amount of radioactive substances attached to it, so it is problematic to dispose of it in the ocean, and currently only storage in hangars is being considered.

If concentrated waste liquid is solidified, the proportion of waste ion-exchange resin in low-level waste is large, and excluding waste ion-exchange resin from items subject to ocean dumping is disadvantageous from the perspective of storage, etc. be.

Therefore, by stripping the cladding from waste ion exchange resin,
Separate and reduce the radioactivity level of waste ion exchange resin,
It is necessary to comply with regulatory standards for waste subject to ocean dumping.

The adhesion of crud to waste ion exchange resin can be roughly divided into two types: one that adheres to the surface of spherical ion exchange resin in the form of a film, and the other that adheres to the surface of spherical ion exchange resin in the form of a filling between particles of ion exchange resin. It is roughly divided into two types:

When these claddings are peeled off, they become very fine particles, with a maximum size of about 100 μm.

In contrast, the particle size of waste ion exchange resin is several hundred micrometers.

In order to selectively separate only minute rads from a slurry consisting of two types of small-diameter particles, a large amount of water is required for discharging the liquid phase containing crud, washing the waste ion exchange resin, etc. .

That is, there is a drawback in that a large amount of water containing radioactive materials is stored in a tank, transported, or water treatment processes such as washing are added.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art as described above, and to provide a method for effectively separating the crud from a slurry of waste ion exchange resin containing the crud and disposing of the waste ion exchange resin. .

The present invention involves transferring granular waste ion exchange resin slurry containing microparticles of cladding to a cladding separation tank, adjusting the pH of the slurry, adding a scavenger, and supplying air from the bottom of the separation tank to create bubbles. The waste ion exchange resin and the crud are separated by causing only the crud in the slurry to adhere to the rising bubbles and floating, and then being discharged outside the crud separation tank, and containing the waste ion exchange resin from which the crud has been separated. The slurry is extracted from the bottom of the tank and dehydrated using a dehydrator, thereby further reducing the radioactivity level.

Embodiments of the present invention will be described below with reference to the drawings.

Analyzing the adhesion of crud to used ion exchange resin from a demineralizer filled with ion exchange resin at a nuclear power plant, it is found that crud is mainly attached to the cation exchange resin, while the adhesion to the anion exchange resin is poor. Very little.

Therefore, by stripping the cladding from the cation exchange resin and separating the cladding, most of the cladding is removed from the waste ion exchange resin, making it possible to significantly reduce the radioactivity level.

The adhesion of the cladding to the cation exchange resin is thought to be due to the fact that the cooling water system is on the slightly acidic side, so iron oxide, the main component of the cladding, becomes positively charged and adheres to the cation exchange resin. .

A beaker experiment was conducted based on the properties of the cladding described above.

That is, water was poured into a glass washing bottle with a filter plate having a capacity of 25 QmJ, and a cation exchange resin (particle size of approximately 500 μm), iron oxide of 100 μm or less, various scavengers, and a pH adjuster (sulfuric acid or caustic soda) were added. Air was supplied to generate bubbles in the water, and the effects of the scavenger and pH on the floating status of iron oxide were investigated.

FIG. 1 is a diagram showing the results. The scavenger is sodium lauryl sulfate (additional amount: 1 x 10 mol//!)
This method most effectively levitated iron oxide, and as shown in FIG. 1, the iron oxide separation rate was about 98% when the pH was 6 or less.

Sodium lauryl sulfate (c 12 H255O4N
a) becomes Na+Cl2H2,SO'' in water and is an anionic scavenger.

The reason why the separation rate of iron oxide is good at pH 6 or lower is that iron oxide is positively charged.

Note that the cation exchange resin was negatively charged and no adhesion to air bubbles was observed.

In reality, cation exchange resins and anion exchange resins are used in a mixed bed, so even if they are separated based on the difference in specific gravity,
The anion exchange resin is mixed into the cation exchange resin, albeit in a small amount.

Therefore, we also attempted to separate anion exchange resin from iron oxide.

The experimental results were similar to those of the cation exchange resin, and no phenomenon of the anion exchange resin adhering to air bubbles was observed.

Similar results were also obtained for used ion exchange resins with attached cladding.

In other words, iron oxide can be well separated from the granular ion exchange resin by lauryl sulfate at pH 6 or lower, regardless of whether the granular ion exchange resin is anionic or cationic or the degree of adhesion of the cladding. found.

This is because the anion exchange resin or the ion exchange resin with the cladding adheres to the air bubbles because the particle size of the granular ion exchange resin is about 500 μm, whereas the iron oxide particles have a microscopic diameter. It is presumed that it would not be possible to float to the surface.

The separation rate of iron oxide is - PH using an anionic collector.
It was found that a pH value of 6 or less is good, but a practical pH value is 3 to 6.

In order to lower the pH value, it is necessary to add an acid, and if an acid is added, the amount of waste will increase due to the salts produced by the neutralization process.

Therefore, it is necessary to perform iron oxide separation without adding salt as much as possible.

For this purpose, as mentioned above, it is practical to use a pH value of 3 to 6, and more preferably to perform iron oxide separation at a pH of about 4.5.

FIG. 2 shows an embodiment of the present invention, in which fine cladding particles are separated and removed from a slurry consisting of fine particles of radioactive cladding and granular waste ion exchange resin (when cations and anions are mixed). This is the process of reducing the radioactivity level of waste ion exchange resin and canning it in drums.

Used waste ion exchange resin (granular, particle size, approximately 500μ
The cladding that has adhered to the surface of (m) or the cladding that has adhered between mutual particles of ion exchange resin is peeled off, and slurry 1 consisting of fine clad particles (100 μm or less) and granular waste ion exchange resin is once slurry-receiving. into tank 2.

This slurry 3 is then transferred to a cladding separation tank 4.

The cladding separation tank 4 has a driving stirring blade 5 in the tank, and has an air supply nozzle 19 near the bottom of the tank, and the air supply nozzle 19 is formed so as to be able to generate air bubbles in the separation tank 4. .

A pH adjuster (sulfuric acid, caustic soda) 20 is placed in the slurry in the clad separation tank 4 to adjust the pH within the range of 3 to 6.

Next, a scavenger 21 is added and air is blown into the slurry through the air supply nozzle 19 to generate bubbles in the slurry.

When air bubbles rise on the slurry surface and fill the cladding separation tank 4, the supply of air is interrupted.

Then, in order to sufficiently attach the cladding microparticles to the surface of the generated bubbles, the stirring blade 5 is rotated, and the cladding microparticles in the slurry and the bubbles are mixed and brought into contact with each other.

When the clad particles are sufficiently attached to the bubble surface, the stirring blade 5
interrupts rotation.

Then, air is again blown into the slurry in the cladding separation tank 4 from the air supply nozzle 19 to generate air bubbles, and the air bubbles that were previously generated and have sufficiently attached the cladding microparticles are removed.
It is pushed out of the crud separation tank 4 and discharged.

When the bubbles to which the clad fine particles are sufficiently attached are discharged to the outside of the clad separation tank 4, the air supply is interrupted again, and the stirring blade 5 is rotated in order to sufficiently attach the clad to the surface of the bubbles, and the slurry is Stir and mix the air bubbles.

As described above, in the clad separation tank 4, the steps of generating bubbles, adhering the clad to the bubbles by rotating the stirring blade 5, and discharging the bubbles to which the crud is attached are sequentially and repeatedly operated, thereby separating fine clad particles. It can be efficiently attached to the surface of bubbles and separated and removed from the slurry.

The bubbles 6 discharged to the outside of the crud separation tank 4 and having a sufficient amount of crud attached thereto are transferred to a bubble breaker 7, where the bubbles are crushed.
A concentrated crud liquid 8 is passed through a filter 9, and only the crud 11 is stored in a tank 12.

The filtered water 10 from the filter 9 is returned to the clad separation tank 4 and used for adjusting the slurry concentration.

On the other hand, the ion exchange resin in the slurry in the cladding separation tank 4 adheres to the bubbles and does not float, so it remains in the cladding separation tank 4.

By repeating the three operations of generating bubbles, stirring and mixing the slurry and bubbles, and discharging the bubbles adhering to the crud in the crud separation tank 4, the crud is separated from the slurry at a separation rate of 95% or more, and the waste ion exchange resin is removed. Slurry remains.

This slurry is extracted from the bottom of the separation tank 4, and the extracted slurry 13 is subjected to a centrifugal dewatering device 14 to separate water 15, and the waste ion exchange resin 16 from which the water 15 has been separated is filled into a drum 17 together with cement 18. Solidify and store.

The cladding separation tank 4 due to the above-mentioned operation is caused by the generation of bubbles,
Since the steps of stirring and mixing using a stirring blade and discharging the bubbles adhering to the crud are repeated in sequence, the efficiency of adhering the crud to the bubbles is high, and the crud in the slurry is separated and removed with a small amount of bubbles.

Therefore, the crud concentration of the crud concentrated liquid 8 discharged from the crud separation tank 4 is high, and the amount of water loaded on the filter 9 can be reduced.

The crud separation tank 4 has a stirring blade 5 in the tank, but even if the stirring blade 5 is not provided, the cladding can be separated at a separation rate of 95%.

In this case, since the degree of contact of the cladding with the bubbles is reduced, the amount of cladding attached to the bubbles is small, and a large number of bubbles are required.

Therefore, the clad concentration of the clad concentrated liquid 8 is lower than that in the case where the stirring blade 5 is provided, and the load on the filter 9 increases.

FIG. 3 shows another embodiment of the present invention, which differs from FIG. 2 in that it is intended to separate only cation exchange resins with a moderate degree of crud adhesion.

When disposing of the ion exchange resin in a nuclear power generation desalination device 30 filled with ion exchange resin, the anion exchange resin 31 and the cation exchange resin 32 are extracted separately.

Since it is generally used in a mixed bed, the difference in specific gravity of both ion exchange resins (anion exchange resin = about 1.1, cation exchange resin - about 1.3 to 1.5) is used to extract them separately. First, only the cation exchange resin 32 to which the cladding is attached is transferred to the slurry receiver tank 33, and this cation exchange resin 3
2 into the clad stripping device 34 to strip the cladding.

Slurry containing cation exchange resin from which the cladding has been peeled 3
5, the slurry receiver is transferred to tank 2.

The slurry containing the peeled microparticles of the cladding and the granular cation exchange resin (approximately 500 μm in particle size) is transferred to the cladding separation tank 4, where the cladding is separated by the same steps and operations as in the embodiment shown in FIG. Separation takes place.

On the other hand, since almost no cladding is attached to the anion exchange resin 31, it is directly transferred to the centrifugal dehydrator 14 without passing through the cladding peeling and separation process, and together with the cation exchange resin 13 from which the cladding has been separated. After the moisture is separated, it is solidified and stored in a drum can 17 with cement 18.

The advantage of the above-mentioned treatment method is that only the cation exchange resin to which the clad is attached is subjected to the clad separation treatment, so that the capacity of the clad separation treatment tank 4 can be small.

Further, the cation exchange resin is easily crushed due to long-term use and operation, and the used waste cation exchange resin contains a considerable amount of crushed fine particles of the cation exchange resin.

Since the cation exchange resin is also negatively charged with respect to the crushed cation exchange resin of these fine particles, only the positively charged cladding can capture the anion type, regardless of the floating by air bubbles. It floats to the surface and is effectively separated and removed by lauryl sulfate, which is an absorbent.

As mentioned above, the specific gravity of ion exchange resins is approximately 1.1 for anion exchange resins and approximately 1.3 to 1 for cation exchange resins.
．． It is in the range of 5.

Therefore, the specific gravity of the anion exchange resin is smaller than that of the cation exchange resin, and is slightly heavier than water.

For this reason, when air bubbles are introduced into a slurry containing an anion exchange resin and stirred to cause the air bubbles to float, some of the anion resin is light and gets caught up in the air bubbles and floats along with the air bubbles. , and may be discharged to the outside of the cladding separation tank together with air bubbles attached to the cladding.

On the other hand, if the cladding of only the cation exchange resin is separated in the cladding separation tank as in this example, since the cation exchange resin is heavy as described above, it is difficult to get caught up in the bubbles, and only the cladding adheres to the bubbles. and is discharged outside the crud separation tank.

Therefore, the ion exchange resin and the cladding are effectively separated, and the ion exchange resin is not mixed into the cladding concentrate.

As described above, the present invention is designed to separate only the cladding by selectively adhering it to air bubbles from a slurry consisting of the cladding of microparticles and the granular waste ion exchange resin, so that the separation process and operation are simple. It is simple, does not require large amounts of water for cleaning to separate the crud, and can reduce the radioactivity level of waste ion exchange resin to meet regulatory standards for waste subject to ocean dumping. .

[Brief Description of the Drawings] Fig. 1 is a diagram showing the relationship between PH and iron oxide separation rate using the scavenger lauryl sulfate; Fig. 2 is a system diagram showing an example of an apparatus implementing the present invention; FIG. 3 is a system diagram showing another example of the device implementing the present invention. 1.3,13,35...Slurry, 2,33.
... Slurry receiver is tank, 4 ... Crud separation tank, 5 ... Stirring blade, 6 ... Air bubbles with crud attached, 7 ...・Bubble breaker, 8...
・Concentrated crud liquid, 9...Filter, 10
, 15...Moisture, 11...Clad,
12... Crud storage tank, 14...
・Dehydration equipment, 16...Waste ion exchange resin, 17
...Drum, 18...Cement, 1
9...Air supply nozzle, 20...PH
Conditioner, 21... Collection agent, 30... Desalter, 31... Anion exchange resin, 32...
...Cation exchange resin, 34...Clad stripping device.

Claims (1)

[Claims] 1 A slurry containing radioactive cladding and waste ion exchange resin is adjusted to pH 3 to 6 in a cladding separation tank, sodium laurate is added as a scavenger, and the cladding separation tank is vented. Air bubbles are generated in the slurry, the cladding adheres to the air bubbles rising in the slurry, floats, and is taken out of the tank.
A radioactive waste treatment method characterized by separating the ion exchange resin and the cladding by extracting the ion exchange resin from the tank. 2. The method for treating radioactive waste according to claim 1, characterized by an ion exchange resin from which the cladding has been separated. 3. The method for treating radioactive waste according to claim 1, wherein the bubbles to which the cladding taken out from the cladding separation tank are broken are filtered and the cladding is stored in a tank. 4. The radioactive waste treatment method according to claim 1, wherein mechanical stirring is performed in the cladding separation tank. 5. The radioactive waste treatment method according to claim 1, wherein the waste ion exchange resin is separated into a cation exchange resin and an anion exchange resin and extracted, and the cation exchange resin is introduced into a cladding separation tank. 6. The radioactive waste treatment method according to claim 5, characterized by comprising a cation exchange resin from which the cladding has been separated and an anion exchange resin that does not undergo a cladding separation step.